1. Field of the Invention
The invention relates to a jointing device for producing a clinching connection between a first workpiece and a second workpiece by means of a plunger which is insertable from above into the recess of a die whose peripheral wall has stationary wall sections which extends substantially parallel to the pressure direction. Moreover, the invention concerns a clinching method in which a first workpiece and a second workpiece with areal portions are placed atop one another at least with partial overlap and the first workpiece is indented from above such that it is imparted with a cup-shaped formed portion which presses into the second workpiece in the downward direction and deforms the latter without cutting, wherein the formed portion of the first workpiece forms an undercut with the second workpiece limited to predetermined peripheral areas of the formed portion. Finally, the invention relates to a clinching connection wherein a first workpiece has a formed portion which engages a formed portion of a second workpiece and forms with the second workpiece an undercut that is limited to predetermined peripheral areas.
2. Description of the Related Art
Such a clinching device, a clinching method, and a clinching connection are known from U.S. Pat. No. 5,230,136. The die has a cylinder-shaped formed portion from which radial channels extend. A plunger which has a somewhat smaller diameter than the formed portion produces during lowering into two stacked workpieces first a cup-shaped formed portion of the two workpieces wherein in the area of the channels the material of the workpieces can be forced slightly outwardly. By doing so, between the material of the upper workpiece and the material of the lower workpiece a slight undercut can be formed, while the formed portion of the lower workpiece has substantially vertically extending wall sections at the exterior.
In the process of clinching, two workpieces are connected to one another by partial deformation. This can be carried out without supplying heat, which is required, for example, for welding or soldering, and without auxiliary means such as adhesives or auxiliary connecting parts (screws or bolts).
The two workpieces must have areal portions for this purpose which must overlap at least partially with one another and which must rest parallel on one another. It is also possible to connect more than two workpieces with one another. For the subsequent explanation it is assumed that the first and the second workpieces are the outer workpieces. Alternatively, each workpiece can form an undercut with the next workpiece.
In connection with the clinching method, a single step method and a double step method are to be differentiated. In the single step method, the clinching connection is generated in a single working step. In the simplest case, a plunger is lowered into a die. By doing so, cup-shaped formed portions result in the two workpieces and are seated in one another with great friction force. Such a connection has a high shearing resistance but only minimal head-on tensile strength.
In order to increase the head-on tensile strength, dies are used in which, for example, the peripheral wall of the recess is formed by lamellas which are secured with respect to their position by an annular spring, for example, an elastomer ring. When the plunger produces the formed portions and is pressed farther with a sufficiently large force into the die, the two workpieces will deform radially outwardly and will accordingly press the lamellas outwardly so that an undercut of the first workpiece is formed in the second workpiece. In this configuration, the head-on tensile strength is substantially increased. However, the die is a relatively complex component. The lamellas must be manufactured with high precision.
An even better head-on tensile strength results during clinching with a cutting component. For this purpose, two cuts are provided at least in the workpiece facing the die. The other, upper workpiece is then deformed such that it penetrates at least partially the cuts. When applying an even higher pressure, the material is then forced through the cuts to the exterior and forms again an undercut. In this connection it is also required to provide the die with lamellas which are pulled or pressed inwardly by means of a spring force. The clinching connection with cutting component has the advantage of a high head-on tensile strength. However, it has the disadvantage that the workpieces must be cut so that it is no longer possible to provide gas and liquid tightness. This disadvantage can be prevented in that the clinching operation is employed with a reduced cutting component, according to which only the workpiece facing the die is provided with cuts. In both cases, the connection is however generally not suitable for dynamically loaded parts because notch effects result due to the cuts.
In addition to the single step method, two-step clinching methods are known which provide improved head-on tensile properties even without a cutting component. However, in this connection it is necessary to transport the workpieces from one tool to the next or, in reverse, to position a second tool on the required position on the workpiece. Both working steps require a relatively high precision during positioning which makes manipulation more difficult.
DE-A-39 23 182 A1 shows a device for connecting plate-shaped components by means of a die which is comprised of two parts connected at their lower end by a tension spring. The die has at its upper end a recess which conically widens in the downward direction. When a plunger, with interposition of two workpieces, is moved into the die, a clinching connection is produced which has an undercut over its entire periphery, i.e., an undercut between the first and the second workpieces and an undercut on the exterior side. For removing the connected workpieces, it is therefore required to pull apart the two die parts. Since this pulling apart is carried out against the force of the spring, there is the risk that the lower workpiece is scratched or damaged.
GB-A-2 069 394 describes a method for jointing plate-shaped workpieces and a device therefor. The device has a die which is formed by four springy portions which in the peripheral direction adjoin one another and surround a recess. The recess widens conically in the downward direction. In the recess, a counter member to a plunger is arranged which is moved downwardly counter to the force of a spring, when a plunger is moved into the die, with interposition of two workpieces. The movement of the counter member stops shortly before the plunger has reached its greatest stroke. By doing so, the two workpieces are pressed together at the end of the clinching process so that the material is forced radially outwardly in order to form undercuts. When removing the connected workpieces, the portions forming the die must be bent away again. Here, there is also the risk that the connected workpieces will become scratched or will be damaged in other ways.
DE-A-44 31 849 describes a clinching method and a clinching tool in which the plunger elements and die elements are arranged on oppositely positioned and synchronously rotating wheels. This allows to produce clinching connections in a continuous process.
It is an object of the invention to provide durable clinching connections which can be realized in a simple way.
This object is solved for a clinching device of the aforementioned kind in that the peripheral wall of the recess has movable wall sections between the stationary wall sections which moveable wall sections are arranged on levers wherein the levers are moveable by pressure from above into a working position and can be secured therein and form undercut areas and, by movement of the connected workpieces in the upward direction, are moved into a release position in which the undercut areas are completely released.
With such a clinching device one obtains first of all a relatively simple configuration of the die. The terms xe2x80x9ctopxe2x80x9d and xe2x80x9cbottomxe2x80x9d are to be understood independent of the direction of the force of gravity in space. They are provided only to determine certain directions relative to the die and to the plunger. For the description of the present invention it is presupposed that xe2x80x9ctopxe2x80x9d is the direction from which the plunger will approach the die. The term xe2x80x9cbottomxe2x80x9d accordingly indicates the opposite direction. By using levers or fingers which are moved by the pressing process itself into their working position and are secured therein, springs or other auxiliary means, which are required to move the die into the closed position required in order to initiate a deformation, are firstly no longer required. At the moment when the two workpieces are placed onto the die and are loaded with pressure, the levers move into their working position. In this working position, they cannot move away because they are secured therein by the workpieces themselves. The undercuts now provide a space into which the material of the two workpieces can flow. Since the material facing the die is pressure-loaded by the material of the other workpiece, not only the material of the lower workpiece flows into the undercut area but it allows also the material of the other workpiece to follow so that the first workpiece forms an undercut with the second workpiece in the sense of a positive-locking hook connection. Usually, for such an undercut, which is also visible at the die side, the removal of the workpiece from the die would present a certain problem. However, according to the invention, this is prevented in that during lifting of the workpiece, more precisely, of the workpieces connected to one another, the lever is pivoted outwardly, i.e., is moved into the release position. When doing so, the lever must not overcome any spring forces which are required usually for its return movement. Accordingly, the removal of the workpieces can be realized with relatively minimal expenditure, for example, by lifting springs or ejectors. An additional advantage is provided in that during removal of the workpieces from the die the levers will not scratch under pressure the underside of the workpieces so that corresponding scratches are substantially avoided. This not only protects the workpiece but also the corresponding contact surfaces of the levers. The clinching connection not only can be produced in a simple manner; it is also very durable and has a head-on tensile strength, shearing strength, torsional strength, and fatigue strength under reversed bending stresses that makes it suitable for automotive construction. The configuration with the movable wall sections and the stationary wall sections which are substantially parallel to the pressure direction has the advantage that the deformation of the two workpieces resulting in the undercuts does not extend uniformly over the entire periphery of the recess of the die. Instead, along the wall of the recess of the die, only individual portions are provided in which an undercut is present. This has, on the one hand, the advantage that the clinching connection has a certain rotational securing action. On the other hand, this has the advantage that the removal, i.e., taking the workpieces out of the die, is simplified. In the wall sections, which extend parallel to the pressure direction, the workpieces can be simply removed from the die in a direction reverse to the pressure direction. Only in the area of the movable wall sections it is required to move the levers outwardly. A further advantage resides in that for the formation of the undercuts more material is available. This makes it possible to enlarge the undercut overlap to the exterior, i.e., perpendicular to the pressure direction. This results from the fact that material can be displaced from the areas with stationary wall sections into the undercuts. For the head-on tensile strength it is generally of greater importance how far the undercuts project radially or perpendicularly relative to the pressure direction than the question how large the undercut areas are in the peripheral direction.
Preferably, the levers have a substantially planar top side which extends in the working position perpendicularly to the pressure direction and is positioned in the same plane as the top side of the die. External to the actual formed portion, with which the clinching connection is produced, the workpiece is thus positioned substantially opposite a continuous and planar surface. External to the actual clinching connection, no markings are thus produced in the surface of the workpieces. Since the levers with their top side form a plane which extends perpendicularly to the pressure direction, pressure peaks on the levers are avoided. The loading is relatively uniform in the working position so that the levers are treated with care and accordingly have a relatively long service life. As long as the levers are not yet in the working position, the different pressure loading ratios are acceptable because only relatively small counter forces act on the levers.
Preferably, each lever is formed as an angled lever. The pressure force which is used for moving and securing the lever in the working position can thus act onto a larger surface area. The leverage is more favorable so that the required forces can be received even with a relatively weakly dimensioned lever.
Preferably, the angled lever has a short arm on which the wall section is arranged and a long arm on which a pivot axis is located. The lever is thus formed in the shape of an L. At the end face of the short leg the wall section is positioned which forms a part of the sidewall of the recess of the die. The forces which act here are introduced via a relatively long lever arm into the pivot axis. When the closing forces now act via a similarly long lever arm, i.e., onto the outer side of the short leg of the xe2x80x9cLxe2x80x9d, a relatively small expenditure provides the desired equilibrium of forces.
The invention operates satisfactorily when two oppositely positioned levers are provided. It is then possible to arrange several clinching connections relatively tightly next to one another. Preferably, at least three levers are however arranged in the peripheral direction of the recess. With three levers, a force distribution in the peripheral direction can be ensured that is uniform and predetermined in all directions.
Preferably, four levers are however provided. This embodiment has advantages with regard to manufacturing-technological considerations. In particular, a certain symmetry can be ensured.
Preferably, the stationary wall sections form at least 50% of the peripheral length of the recess. The undercut areas are thus relatively short with respect to the peripheral direction. Accordingly, only finger-like or ray-like undercut areas result which have a relatively large depth perpendicularly to the pressure direction.
Advantageously, the die has for each of the levers a securing device against falling out. This securing device against falling out has two advantages. On the one hand, when removing the workpieces from the die it is no longer required to pay attention to the levers remaining in the die. They are instead secured by the securing device against falling out. On the other hand, the die can also be used xe2x80x9coverheadxe2x80x9d, i.e., the plunger can be moved against the force of gravity toward the die. This provides a greater flexibility relative to the mounting position when operating the device.
In a preferred embodiment, the securing device against falling out is a nose which acts radially in the direction toward the lever wherein the lever has a notch cooperating with the nose. This takes into account that the securing device against falling out must be active only when the lever is in its release position. In this position the nose engages the notch and prevents a further movement of the lever in the upward direction, i.e., out of the die. When, in contrast thereto, the levers are in their working position, then they are secured therein by the workpieces. The exchange of the levers, which form the wear parts of the die, is relatively simple. The levers (without contact on the workpieces) must be pivoted in their working position and they can be removed from the die when in this position.
Preferably, the nose has at its upper side a guide surface on which the lever glides during its movement. With this embodiment, it is possible that the lever during its movement from the working position into the release position is not only pivoted but also at the same time displaced parallel to the pressure direction. This realizes a larger opening width so that, in turn, the undercut can have a greater depth. This, in turn, results in a higher head-on tensile strength of the connection.
Advantageously, the nose is formed in an insert part. Then it is possible to employ the nose for the purpose of securing the lever in the die in a captive way. For exchanging the levers, it is only required to demount the insert part which is however possible with relatively minimal expenditure.
In an alternative embodiment, the securing device against falling out is a pin which is guided through the die and the lever and which forms a pivot axis. In this case, the levers are also secured in the die in a captive way. For mounting the lever it is only required to insert the levers into the die and to then insert the pin.
Preferably, the recess has a bottom which is arranged at the upper side of a bottom part inserted into the die. The bottom of the die, which is conventionally provided with a certain shaping in order to ensure flowing of the materials of the workpieces into the corresponding edge areas of the recess, is a wear part. The flowing of the materials takes place with considerable friction. The possibility of arranging the bottom on a bottom part which is exchangeable makes it possible to keep the maintenance and service expenditures of the die relatively small. The levers and the bottom which, as mentioned above, form the main wear parts can be exchanged with simple measures. The bottom part can be secured stationarily in the die.
Advantageously, several dies are arranged adjacent to one another on a first support and several plungers are arranged adjacent to one another on a second support with the same division, wherein at least one of the two supports can be moved relative to the other support such that the plungers and the dies will engage one another successively. The same division can be achieved mechanically in that the plungers and dies have the same center spacing relative to one another. However, it can also be achieved by a suitable movement control. With such a device a series of adjacently positioned clinching connections can be produced quasi continuously. The workpieces are guided between the two supports wherein the two supports have an engagement position where the plunger will engage a die. At this location, the clinching connection is then produced. By a further movement of the workpiece and of the supports, the plunger is then removed from the die and the next plunger enters the next die.
In this connection, it is preferred that at least one support is formed as a wheel and the other support is formed with a planar surface. The wheel can then, so to speak, roll on the surface wherein it may also be provided that the wheel has a stationary rotational axis and the support is moved past it.
In an alternative embodiment, both supports can be formed as a wheel. At the surfaces of both wheels plungers or dies are then provided which engage one another successively.
In another especially preferred embodiment, adjacently positioned dies have lever arrangements which differ from one another. Accordingly, the clinching connections produced adjacent to one another have different orientations and/or shapes. This increases the strength of the connection. In particular, with this it can be realized that the connection between the workpieces has an increased loadability in several directions. It is possible to produce framework-like structures which provide a high torsional stiffness to the connected parts.
This is achieved in a preferred embodiment in that the lever arrangements are arranged asymmetrically wherein the lever arrangements of neighboring recesses are rotated relative to one another. By doing so, adjacently positioned clinching connections also are provided with an asymmetric appearance, i.e., they no longer have radial symmetry relative to an axis which is perpendicular to the workpieces. When now clinching connections positioned adjacent to one another are moreover rotated relative to one another, the strength is improved in different directions.
It is especially preferred in this connection that per recess only one lever is provided. This simplifies the configuration of the die considerably.
The object is solved for a method of the aforementioned kind in that the second workpiece is formed with an outer shape having an undercut in the peripheral areas with undercut between the first and the second workpieces.
Several advantages are obtained according to this procedure, as explained above in connection with the device. On the one hand, when producing the clinching connection, a rotational securing action is automatically provided even when the formed portion otherwise is of radial symmetry. By means of the outwardly projecting undercut areas, which do not extend over the entire periphery, a rotational movement of the two parts relative to one another is blocked. It is especially advantageous in this connection that for the manufacture of the undercut areas more material is now available. In other words, the material which is conventionally available over the entire periphery of the formed portion can now be concentrated onto only a few undercut areas. This makes it possible to make the undercuts wider or deeper perpendicularly to the pressure direction with the same amount of material. It was found that the strength of the connection depends to a greater degree on the depth of the undercuts than on the length of the undercuts in the peripheral direction. When the undercuts are thus limited to areas of the peripheral direction and these areas are then designed with greater overlap in the undercut area, the connection is then as a whole strengthened. This achieves, despite a single-step method and without cutting component, connecting qualities which are otherwise achievable only by two-step methods or by clinching methods with a cutting component. However, the connections formed according to the invention are also dynamically loadable.
Preferably, between the peripheral areas on an exterior side of at least one workpiece, wall sections are produced which extend parallel to the pressure direction. This embodiment entails a compromise. On the one hand, the removal from the die, i.e., taking the workpieces out of the die, is still easily possible. In the areas where the outer side extends parallel to the pressure direction no deformation work must be provided any longer in order to remove the workpiece. Only the frictional forces must be overcome. On the other hand, in particular, for at least substantially vertical peripheral walls, the material constellation is such that the optimal flow paths for the two materials of the workpieces into the undercut areas are provided.
Preferably, a closing force is generated during indenting which acts at least onto one tool part and an opening force results during removal of the formed workpieces from the tool part. Accordingly, the method becomes quasi self-controlling. No external means are required any longer for moving the tool part into its working position or for providing an opening of the tool part when removing the workpieces.
Advantageously, three or more undercut peripheral areas are produced. By doing so, a connection that is supported on all sides perpendicular to the pulling force can be achieved.
The object is solved for a clinching connection of the aforementioned kind in that the second workpiece in the area of the undercut with the first workpiece has an outer shape with an undercut.
As discussed above, in this way it is possible to provide an undercut depth, i.e., the depth of the positive-locking hook connection, is greater than previously. The required material for this can originate in the areas in which no undercut is present. By the shaping at the active surfaces of the levers forming the undercuts, the flow properties can be optimized with regard to the workpieces to be connected. The size and the location of the positive-locking hook connection can be optimized and defined by the selection of the predetermined peripheral areas and the undercut depth.